Stent catheter with a permanently affixed conductor

ABSTRACT

A stent assembly is provided. A conductor which is permanently affixed to a catheter contacts a stent mounted on the catheter. Conductive ink applied to the catheter may be used as the conductor. A method of coating the stent is also provided. In the method, an electrical charge is applied to the conductor. The stent is then coated using an electrostatic coating process.

BACKGROUND

The present invention relates generally to medical devices andparticularly to a catheter used to implant stents which has apermanently affixed conductor.

The use of stents to treat various organs, such as the vascular system,colon, biliary tract, urinary tract, esophagus, trachea and the like,has become common. Typically, stents are useful in treating blockages,occlusions, narrowing ailments and other similar problems that restrictflow through a passageway.

One common medical treatment in which stents are used involvesimplanting an endovascular stent into the vascular system. Stents areuseful for numerous medical treatments of various vessels throughout thevascular system, including both coronary vessels and peripheral vessels(e.g., carotid, brachial, renal, iliac and femoral). However, the use ofstents in coronary vessels has drawn particular attention from themedical community due to the commonality of heart problems caused bystenosis (i.e., narrowing of a vessel).

Although stenosis may occur for a variety of reasons, one of the mostcommon causes of coronary stenosis results from the buildup ofatherosclerotic plaques along the lumen of the vessel. The resultingcoronary stenosis restricts blood flow through the vessel, whicheventually can lead to a dangerously increased risk of heart attacks.

The medical community has attempted to address coronary stenosis (alongwith the many other passageway problems that patients suffer from) withvarious versions of percutaneous transluminal angioplasty (“PTA”).Fundamentally, PTA involves inserting a balloon-tipped catheter into avessel and threading the catheter to the narrowed portion to be treated.The balloon is then expanded at the narrowed portion by pumping salinethrough the catheter to the balloon. As a result, the balloon expands,contacts the inner vessel wall, and forces the vessel to dilate. Theballoon is then deflated and retracted from the vessel.

One problem that has been encountered with typical PTA procedures isrestenosis (i.e., re-narrowing) of the vessel. Restenosis may occur fora variety of reasons, such as collapsing of the vessel wall or growth ofcellular tissue. For example, restenosis may occur due to damage causedto the vessel lining during balloon expansion and vessel dilating. As aresult of the damage caused to the intima layers of the vessel, thevessel attempts to grow new intima tissue to repair the damage. Thistendency of vessels to regrow new tissue is referred to as neointimalhyperplasia. The effect of this response results in a re-narrowing ofthe vessel. However, restenosis is not completely predictable and mayoccur either abruptly soon after the PTA procedure due to vesselcollapse or may occur slowly over a longer period of time due to otherreasons.

One approach the medical community has tried in order to overcome theproblems with restenosis is to use stents in conjunction with theabove-described PTA procedure. Traditionally, stents are made of metalor other synthetic materials, thereby providing a tubular supportstructure that radially supports the inner wall of the vessel. Althoughother materials are possible and are sometimes used, the most commonmaterials now used in stents are stainless steel (e.g., 316L SS and 304SS) and Nitinol. Typically, stents are designed with a pattern ofopenings formed in the support structure that permits the stent toradially expand from a small diameter to a larger diameter. Accordingly,stents are now commonly used in conjunction with conventional PTAprocedures by positioning the stent within the portion of the vesselthat has been dilated by the balloon and radially expanding the stentagainst the inner wall of the vessel to permanently implant the stent.The expectation of this revised PTA procedure is that the supportstructure of the implanted stent will mechanically prevent the vesselfrom collapsing back to its original narrowed condition.

Although stent designs and implantation procedures vary widely, twocategories are common.

The first of these two categories may be referred to asballoon-expandable stents. Balloon-expandable stents are generally madefrom ductile materials that plastically deform relatively easily. In thecase of stents made from metal, 316L stainless steel that has beenannealed is a common choice for this type of stent. One common procedurefor implanting a balloon-expandable stent involves mounting the stentcircumferentially on the balloon prior to threading the balloon-tippedcatheter to the narrowed vessel portion that is to be treated. When theballoon is positioned at the narrowed vessel portion and expanded, theballoon simultaneously dilates the vessel and also radially expands thestent into the dilated portion. The balloon and the catheter are thenretracted, leaving the expanded stent permanently implanted at thedesired location. Ductile metal lends itself to this type of stent sincethe stent may be compressed by plastic deformation to a small diameterwhen mounted onto the balloon. When the balloon is then expanded in thevessel, the stent is once again plastically deformed to a largerdiameter to provide the desired radial support structure. Traditionally,balloon-expandable stents have been more commonly used in coronaryvessels than in peripheral vessels due to the deformable nature of thesestents. One reason for this is that peripheral vessels tend toexperience frequent traumas from external sources (e.g., impacts to aperson's arms, legs, etc.) which are transmitted through the body'stissues to the vessel. In the case of peripheral vessels, there is anincreased risk that an external trauma could cause a balloon-expandablestent to once again plastically deform in unexpected ways withpotentially severe and/or catastrophic results. In the case of coronaryvessels, however, this risk is minimal since coronary vessels rarelyexperience traumas transmitted from external sources.

A second common category of stents is referred to as self-expandablestents. Self-expandable stents are generally made of shape memorymaterials that act like a spring. Typical metals used in this type ofstent include Nitinol and 304 stainless steel. A common procedure forimplanting a self-expandable stent involves a two-step process. First,the narrowed vessel is dilated with the balloon as described above.Second, the stent is implanted into the dilated vessel portion. Toaccomplish the stent implantation, the stent is installed on the end ofa catheter in a compressed, small diameter state and is retained in thesmall diameter by inserting the stent into the lumen of the catheter orby other means. The stent is then guided to the balloon-dilated portionand is released from the catheter and allowed to radially spring outwardto an expanded diameter until the stent contacts and presses against thevessel wall. Traditionally, self-expandable stents have been morecommonly used in peripheral vessels than in coronary vessels due to theshape memory characteristic of the metals used in these stents. Oneadvantage of self-expandable stents for peripheral vessels is thattraumas from external sources do not permanently deform the stent.Instead, the stent may temporarily deform during an unusually harshtrauma but will spring back to its expanded state once the trauma isrelieved. Self-expandable stents, however, are often considered to beless preferred for coronary vessels as compared to balloon-expandablestents. One reason for this is that balloon-expandable stents can beprecisely sized to a particular vessel diameter and shape since theductile metal that is used can be plastically deformed to a desired sizeand shape. In contrast, self-expandable stents are designed with aparticular expansible range. Thus, after being installed self-expandablestents continue to exert pressure against the vessel wall.

However, even when a stent is used in conjunction with conventional PTAprocedures, restenosis still remains a problem. As discussed above, onecause of restenosis is neointimal hyperplasia which may result fromdamage to the vessel wall. This cause of neointimal hyperplasia remainsa problem even when a stent is used. In addition, the syntheticmaterials that are usually used in stents may also contribute toneointimal hyperplasia. The cause of this problem is the body's tendencyto grow new living tissues around and over newly implanted foreignobjects. Thus, despite the mechanical support structure provided by thestent, restenosis remains a problem.

One approach that has been offered to address the problem of restenosishas been to coat stents with drugs that are designed to inhibit cellulargrowth. Although many such drugs are known, common examples of thesetypes of drugs include Paclitaxel, Sirolimus and Everolimus. However,despite the benefits of these types of drugs, numerous problems stillexist with the current methods that are used to apply these and othercoatings to stents.

Typically, a stent is provided by the manufacturer as part of apre-assembled package. For example, in the case of a balloon-expandablestent, the package may include a catheter, a balloon formed at the endof the catheter, and a drug-coated stent mounted onto the balloon. Inthe case of a self-expandable stent, the package may include a catheter,a mounting apparatus for retaining and releasing the stent, and adrug-coated stent mounted on the apparatus.

One method that may be used to manufacture the above-described stentassemblies involves coating the stent first in a separate step and thenmounting the coated stent onto the balloon or other mounting apparatus.Common coating processes include dipping, spraying and painting the drugonto the stent. However, these methods suffer from numerous problems.One problem is the difficulty of mounting the coated stent onto thecatheter without damaging the coating that has been applied. Inaddition, many conventional coating processes are difficult to controland apply an uneven coating on the stent. Moreover, when the stent iscoated separately, it is difficult to avoid coating at least part ofboth the inside and outside surfaces of the stent.

Alternatively, the stent may be coated after being mounted onto thecatheter. However, this method has not been perfected. As mentioned,conventional coating processes are difficult to control and apply unevencoatings. This can be an even more significant problem when the coatingis applied to a stent mounted to a catheter since the coating inevitablyends up coating the catheter, balloon and/or mounting apparatus also.

Precisely controlling the application of coatings on stents is importantfor a number of reasons. For example, in the case of drug coatings inparticular, it is important to ensure that the drug is applied as evenlyas possible on the specific surfaces where the coating is needed. Thisensures a uniform physiological response to the drug after the stent isimplanted. Another important reason for precisely controlling theapplication of coatings is the high cost of many coatings. Typically, inthe case of drug coatings, the cost of the drug per unit volume can bevery expensive. Therefore, the drug should be applied as precisely aspossible to the surfaces of the stent where the effectiveness of thedrug can be maximized. Thus, by minimizing waste during the coatingprocess, the overall cost of the stent assembly may be reduced.

It is apparent to the inventor that a stent assembly is desired in whichcoatings may be applied to the stent in a more effective manner than ispresently possible. Accordingly, a solution is described more fullybelow that solves this and other problems.

SUMMARY

A stent assembly is provided with a conductor that is permanentlyaffixed to a catheter. Preferably, the conductor is applied to theexterior of the catheter using conductive ink. The conductor extendslongitudinally along the catheter and contacts the stent. One advantageof the conductor is that the stent assembly may be coated with drugs orother coatings using an electrostatic coating process. During theelectrostatic coating process, the conductor is grounded or connected toan opposite electrical charge, thereby providing electrical attractionbetween charged coating particles and the stent. Additional details andadvantages are further described below.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention may be more fully understood by reading the followingdescription in conjunction with the drawings in which:

FIG. 1 is a side view of a catheter with a balloon and stent located ata distal end thereof, showing an electrostatic coating process; and

FIG. 2 is a close-up side view of a portion of the catheter, showing theballoon and the stent with a conductor extending along a portionthereof.

DETAILED DESCRIPTION

Referring now to the figures, a stent assembly 10 is provided for use inpercutaneous transluminal angioplasty (“PTA”) procedures. The stentassembly 10 is provided as a pre-assembled package with the stent 16mounted onto a balloon 14 which is formed at the end of a catheter 12.Although not shown, the principles taught herein may also be adapted toa self-expandable stent assembly in which the stent is mounted on amounting apparatus that selectively retains and releases the stent.

The catheter 12 includes a conductor 18 that is permanently affixed tothe catheter 12. As shown, the conductor 18 is affixed to the outersurface of the catheter 12 and extends longitudinally along a portion ofthe catheter 12. The conductor 18 may extend along the full length ofthe catheter 12, or the conductor 18 may extend as little as an inch orless along the catheter 12. The conductor 18 may also extend along aportion of the balloon 14. At one end, the conductor 18 contacts aninner surface of the stent 16. Since the stent 16 is metallic, anelectrical connection is made between the stent 16 and the conductor 18.

In the preferred embodiment, the conductor 18 comprises conductive inkthat is applied to the exterior of the catheter 12 and balloon 14 as astripe. One type of conductive ink that may be used is a silver-basedepoxy ink. Conductive ink of this type may be obtained from CreativeMetals Incorporated as product number CMI 119-21 and referred to asPrintable Solvent Resistant Electrically Inductive Ink. However,numerous other types of conductive ink may also be used, such asplatinum-based, gold-based and copper-based inks. Non-epoxy inks mayalso be used, such as urethane inks. In general, any compound which maybe applied in a liquid or gel form and is capable of conducting anelectrical current after application may be considered conductive ink.Moreover, the conductor 18 may also comprise any other conductivematerial, such as conductive polymers.

The conductive ink may be applied to the catheter 12 and balloon 14 witha variety of printing processes, such as pad printing, ink jet printing,spraying, marker striping, painting or other like processes. However,pad printing is preferred since it is relatively easy with this processto apply a consistent ink stripe on the catheter 12 and balloon 14.

An advantage of the conductor 18 is that coatings 24 may be applied tothe stent 16 with electrostatic coating processes instead ofconventional coating processes. As shown in FIG. 1, an electrostaticspray nozzle 20 charges the coating material and dispenses chargedcoating particles 22 towards and around the stent 16. Examples ofelectrostatic coating processes that may be used are described in U.S.Pat. Nos. 4,749,125; 5,165,601; 5,086,973 and 5,332,154, which are allhereby incorporated by reference herein. Other electrostatic coatingprocesses may also be used, and any coating process that electricallycharges the coating material may be adapted for coating the stent 16. Anelectrical charge is also applied to the conductor 18 by eithergrounding the conductor 18 or by connecting the conductor 18 to a chargethat is opposite to the charge of the coating particles 22. Thus, thecharged coating particles 32 become electrically attracted to the stent16. As a result, the coating particles 22 are drawn to the surfaces ofthe stent 16 and adhere to the stent 16 once contact is made. Thecoating 24 that results is considerably more consistent and uniform thancoatings applied by conventional processes. The conductor 18 may begrounded 26 in any manner known to those in the art. For example, theconductor 18 may be grounded 26 by the fixture that holds the stentassembly 10 during the coating process. Collets or other knownarrangements may be readily adapted to serve as a ground 26 for theconductor 18. Likewise, the conductor 18 may be connected to an oppositecharge in any manner known in the art.

Electrostatic coating offers significant improvements over conventionalcoating processes, such as dipping, spraying and painting. One of thebenefits of electrostatic coating is that the application of the coating24 can be precisely controlled. Thus, in the case of drug coatings, aprecise amount of the therapeutic agent can be applied uniformly overthe stent 16 without the inconsistencies and waste of conventionalprocesses. This is particularly helpful when typical anti-restenosisdrugs are used since these drugs can be especially expensive. Othercoatings 24 however may also be applied to the stent 16, such ashydrophilic coatings, with similar benefits.

There are also several advantages of coating the stent 16 after thestent 16 has been mounted to the catheter 16 as compared to separatelycoating the stent 16. One benefit is that damage to the coating 24 canbe minimized since the manufacturer does not need to handle an alreadycoated stent when mounting the stent 16 to the balloon 14. Anotherbenefit is that the coating 24 is applied only to the outside surface ofthe stent 16 instead of being applied partially to the inside of thestent 16 as may occur when the stent 16 is coated separately. In thecase of anti-restenosis drugs, this is a more efficient result since theanti-restenosis drug is primarily needed on the exterior surfaces of thestent 16 where the stent 16 contacts the vessel wall after implantation.Although the electrically charged coating particles 22 will be attractedprimarily to the metallic stent 16 as compared to the non-metallicballoon, some of the drug coating 24 (or any other coating used) can beexpected to pass through the openings in the stent 16 and adhere to theballoon 14 instead of the stent 16. However, even these balloon-coatedportions may provide some benefits since these coated portions maycontact the vessel wall during balloon expansion, thereby beingtransferred to the vessel wall.

A further advantage of the conductor 18 is that it is permanentlyaffixed to the catheter 12. One alternative approach that could be usedto electrostatically coat a stent 16 involves positioning a loose groundwire under or adjacent the stent 16 to make an electrical connection.However, this approach is undesirable because the loose wire may beinadvertently left attached to the stent assembly 10 after coating. Thiscould have serious consequences if the loose wire is not removed priorto a surgeon using the stent assembly 10 in a PTA procedure. Inaddition, even when the wire is properly removed during manufacturing ofthe stent assembly 10, the removal step could damage the stent assembly10. One possible risk is that the wire might puncture the balloon 14. Inaddition, removal of the wire may dislodge some of the coating 24.

The conductor may also provide other advantages as well. For example,the conductor 18 may improve visualization of the catheter 12 and stentassembly 10 during implantation by showing up more distinctly in imagingdevices. Moreover, if the conductor 18 is extended along the entirelongitudinal length of the catheter 12, the conductor 18 could be usedduring PTA or other surgical procedures to supply electrical current tothe internal area of the body that is being treated.

It is now apparent that there are many advantages of the inventionprovided herein. In addition to the many advantages that have beendescribed, it is possible that there are other advantages of theinvention that are not currently recognized but which may becomeapparent at a later time.

While a preferred embodiment of the invention has been described, itshould be understood that the invention is not so limited, andmodifications may be made without departing from the invention. Thescope of the invention is defined by the appended claims, and alldevices that come within the meaning of the claims, either literally orby equivalence, are intended to be embraced therein.

1. A stent assembly, comprising: a catheter, and a stent mounted at adistal end of said catheter, wherein said catheter comprises a conductorcontacting said stent and extending longitudinally along at least aportion of said catheter, said conductor being permanently affixed tosaid catheter.
 2. The stent assembly according to claim 1, wherein saidconductor comprises conductive ink applied to said catheter.
 3. Thestent assembly according to claim 2, wherein said conductive ink isapplied by pad printing.
 4. The stent assembly according to claim 1,wherein said conductor is one of silver-based, platinum-based,gold-based and copper-based.
 5. The stent assembly according to claim 1,further comprising a balloon located at said distal end of saidcatheter, said stent being mounted onto said balloon.
 6. The stentassembly according to claim 5, wherein said conductor extends along aportion of said balloon.
 7. The stent assembly according to claim 1,wherein said stent is metallic.
 8. The stent assembly according to claim1, wherein said conductor contacts an inner surface of said stent. 9.The stent assembly according to claim 1, wherein said conductor isdisposed on an outer surface of said catheter.
 10. The stent assemblyaccording to claim 1, wherein said stent is coated with anelectrostatically applied coating.
 11. The stent assembly according toclaim 10, wherein said coating is a drug.
 12. The stent assemblyaccording to claim 1, further comprising a balloon located at saiddistal end of said catheter, said stent being mounted onto said balloon;wherein said conductor comprises conductive ink applied to saidcatheter; said conductor is disposed on an outer surface of saidcatheter; said stent is metallic; and said stent is coated with anelectrostatically applied coating.
 13. The stent assembly according toclaim 12, wherein said conductive ink is applied by pad printing; saidconductor extends along a portion of said balloon; and said conductorcontacts an inner surface of said stent.
 14. The stent assemblyaccording to claim 13, wherein said conductor is one of silver-based,platinum-based, gold-based and copper-based, and said coating is a drug.15. The stent assembly according to claim 1, wherein said conductorcomprises conductive ink applied to said catheter, and said conductor isdisposed on an outer surface of said catheter.
 16. The stent assemblyaccording to claim 1, further comprising a balloon located at saiddistal end of said catheter, said stent being mounted onto said balloon;wherein said conductor comprises conductive ink applied to saidcatheter; said conductor is disposed on an outer surface of saidcatheter; and said conductor extends along a portion of said balloon.17. A method of coating a stent, comprising: permanently affixing aconductor to a catheter, said conductor extending along a longitudinalportion of said catheter; mounting a metallic stent on said catheter,wherein said metallic stent contacts said conductor; electricallycharging a coating material and dispensing said charged coating materialin proximity to said metallic stent; and applying an electrical chargeto said conductor, wherein said charged coating material is attracted tosaid metallic stent, whereby said metallic stent is electrostaticallycoated with said coating material.
 18. The method according to claim 17,wherein said conductor comprises conductive ink applied to saidcatheter, and said conductor is disposed on an outer surface of saidcatheter.
 19. The method according to claim 18, wherein a balloon islocated at a distal end of said catheter, said stent being mounted ontosaid balloon, and said conductor extends along a portion of saidballoon.
 20. The method according to claim 19, wherein said conductiveink is applied by pad printing, and said conductor contacts an innersurface of said stent.